Emergency circumstances occur when a person or persons are buried under rubble. These circumstances can arise from a variety of events, including but not limited to: earthquakes; intentional or unintentional explosions; structural failures due to age, weather, and/or stresses; hurricanes; tsunami tidal waves; etc. The composition of rubble may include but not be limited to: building structures and/or earth and stone.
Locating people buried in rubble after a disaster is difficult, and yet time is precious in order to preserve life. Sniffer dogs are used with limited success. Radar Systems designed to emit and detect electromagnetic waves that penetrate rubble can be useful, however they are prohibitively expensive. In less developed countries, few if any such radar systems are typically available. A cell phone in proximity to a trapped victim can be located by sensing systems as long as its battery lasts. Even then, a cell phone that is transmitting does not necessarily indicate that its user is alive. Given the tremendous effort, resources, time, and risk that are required to attempt to uncover each victim, it is preferable that a cell phone can indicate the presence of life, and most importantly that its battery lasts as long as possible.
Cell phones consume the greatest amount of power when transmitting, so minimizing transmission duty-cycle and transmission signal strength will preserve battery life. Also, a cell phone will increase its transmission strength and power consumption as well as the power consumption of its receiver circuitry when it “thinks” it is farther from a cell tower. Receiver circuits usually consume more power when placed into modes with the purpose of improving sensitivity and signal-to-noise ratio. Thus, if cell towers are non-functional after a disaster, or if a trapped individual's phone thinks it is a long distance from a tower because of signal attenuation through rubble, the phone may increase its transmission signal strength and receiver circuit sensitivity accordingly, and use up its battery charge prematurely.